ICD-11 MMS Implementation in Rare Disease Registries: Quantifying Coding Completeness and Statistical Reliability

Introduction: Epidemiological data on rare diseases (RDs) affect the accurate scientific assessment of these diseases and lead to many issues in policy-making, healthcare systems, and legislation. The coding system is crucial for accurately identifying and calculating the incidence rates of each RD. This study focuses on the effectiveness of collecting RD data via the ICD-11 and examines whether the ICD-11 can fully support RD statistics. The findings of this study should provide a foundation for replacing the ICD-10 with the ICD-11. Methods: This study included 121 RDs from the first “Rare Disease Catalogue”in China.The diseases were recoded independently by two experts in the ICD-11 MMS. A comparative analysis was conducted on the distributions of chapters, code types, and index terms in the ICD-10 and ICD-11 MMS. Results: This study included 121 RDs (69.4% of disease types were disorders, 32.3% were autosomal recessive, and 28.1% were all age-onset) from the first “Rare Disease Catalogue”in China. The 121 RDs had 204 ICD-10 codes, 37.3% (76) of which were non-index terms, and 171 ICD-11 MMS codes. The percentage of RD codes in the ICD-11 was 0.96%, whereas it was 1.4% in the ICD-10, indicating that RDs were less diluted in the ICD-11 (P<0.001). All codes had indices (100% in ICD-11 vs. 62.7% in ICD-10, P<0.001), and 29.8% of the codes (n=51, P<0.001) had more detailed classifications. When using the ICD-11 to code RDs for subsequent statistical analyses, it is recommended that a network system of RD index terms be established in advance. Conclusion: The ICD-11 can replace the ICD-10 for coding RDs. However, many RD terms do not have accurate codes and must be uniquely identified with URIs in the ICD-11. To ensure the reliability of RD-related data, establishing a local RDdatabase for reporting data via the ICD-11 in China is essential.